ZF Friedrichshafen AG has been involved with transmission systems since the beginning, in 1915, when it built propeller drives for Zeppelin airships. It now develops and produces transmissions, steering systems, axles and chassis components as well as systems for cars, trucks and off-road equipment. Also produced are transmission systems for marine craft, rail vehicles and helicopters. ZF is now a worldwide organisation employing more than 33,000 people that is billed as “the world’s largest independent specialist for drive train and chassis technology”.
Total group sales last year were DM10.4bn ($5bn), with the construction machinery and special vehicle sectors accounting for 6% and 1% of that figure respectively. Transmissions used in cranes come from the special vehicle drive systems division at the Friedrichshafen plant in Germany, close to Lake Constance and Switzerland.
A trend is gathering pace in commercial vehicles towards the use of fully automatic transmissions instead of traditional manual gearboxes. Dispensing with a clutch pedal makes driving a two pedal operation, as in an automatic car. Automatic transmissions have advantages over manual types, according to ZF board member and executive vice president of the commercial vehicle division Wolfgang Vogel. Service life is much longer, he says, because it is not dependant on the driver’s skill at shifting gears. It is not possible to crunch gears or burn out the clutch – there is electronic protection against mishandling. Other advantages include direct cost savings – it is cheaper to produce an auto shift gear system than a manual one, and fuel consumption figures are much better. Fuel savings from an automatic ZF transmission over manual are claimed to be between 15% and 40%, depending on the gearbox being replaced.
Automatic transmissions are gaining popularity to such an extent that ZF expects them to be going into as much as 70% of Western Europe’s light duty (up to 6.5t) commercial vehicle production by 2007 and for them to account for 50% of production at the Friedrichshafen plant by 2005. (Last year’s production at that plant totalled 126,000 units). Volume production of the AS Tronic automatic transmission for all-terrain cranes is now starting. Next year ZF says it will deliver 600 units of the AS Tronic and by 2002 the company expects this figure to have reached a thousand units a year.
The first crane to use the AS Tronic system is Liebherr’s five-axle (three or four driven) 100t capacity LTM 1100/2 all-terrain. Bernd Kownatzki, responsible for sales and applications in the ZF special vehicles division, handles the relatively low volume products – 600 units a year for a particular transmission is a big order, and even one offs are not a problem, he says. A lower price than competitors such as US manufacturer Allison is possible right down to a volume of 10 units, Kownatzki claims.
Liebherr will take 40 units this year for the LTM 1100/2 and, having already got orders for 120 units of the new crane, at least a further 80 next year. The LTM 1100/2 uses the ZF AS Tronic model 16 AS 2601, a 16 gear automated synchromesh transmission with electronically controlled clutch and an intarder retarder. A fuel saving of 20% can be expected on the LTM 1100/2 with the new transmission, according to ZF group vice president Reinhard Buhl.
In future Liebherr will be using more of this type of transmission on other all-terrain cranes. Next application for it will be the new 50t capacity LTM 1050/2, to be shown at the Bauma construction equipment exhibition in Munich next March. This crane will use a 12 speed version of the AS Tronic, the 12 AS 2302. Also at Bauma, and using the same 16 speed transmission as the 100 tonner, will be a new five axle 200 tonner, the LTM 1200/1. Deliveries of this crane are planned to start in September next year.
Other crane manufacturers are also interested in the AS Tronic. Tadano Faun will use it on a four-axle truck crane under development for the US market. It will use the 12 speed 12 AS 2302 transmission like the one to be used in the new 50t Liebherr. Tadano Faun in Germany is developing the carrier and Tadano in Japan is working on the crane element.
A 12 speed AS Tronic system is also being developed for a new four axle Grove crane.
Also in the ZF pipeline is a larger 12 speed transmission that can be combined with a torque converter, suitable for use on cranes and other vehicles with six axles or more. The 12 AS 3001 is projected to be ready in 2002.
ZF sees itself as a pioneer in the transmission field to such an extent that it does not expect an equivalent from main competitor Allison for five or six years. Much of the secret lies in the computer software which is used to control shifting patterns and engine speed, among other things, via data bus systems. All diesel engine manufacturers now use data bus technology on their engines and ZF works with them to integrate its control and bus technology to form a seamless package. Matching the engine and transmission software is a bigger job than mechanically mating the engine and transmission. Significant investment is needed as different software has to be developed for each engine manufacturer. Prices come down, however, as more vehicle manufacturers pick up on the idea and volumes increase. The bus system and/or control software used in a crane is different from that used in a truck. Liebherr uses its own LSB (Liebherr System Bus) on the crane, and a CAN bus system for engine management control of the 404kW Liebherr D 9048 TI-E turbocharged diesel in the carrier of the LTM 1100/2.
All electronic hardware is mounted on board the AS Tronic to make it an integrated unit. There are only two plug connectors – one for the vehicle interface, and one for extra functions on the ZF transmission such as an intarder. The intarder, fitted to the transmission of the Liebherr LTM 1100/2, is a pneumatically actuated transmission brake to slow the vehicle down. It reduces wear on the conventional wheel brakes and increases safety by lowering the risk of brake fade from overheating.
An important design feature of the AS Tronic is that it has a dry clutch but no torque converter, unlike competitors. It has pneumatic shifting cylinders, powered by a compressor on the engine. Gear shifting is electronically controlled and fully automated via a Bosch clutch actuator mounted on the underside of the transmission. Full automation makes the system “always right” unlike in a partly automated system. The appropriate gear is selected by the software according to travel conditions but, for example, on rough ground the driver can select a particular gear using pushbuttons in the cab. No adjustment is needed as clutch clearance is measured by a sensor so that the actuator has a reference from which the amount of slip or engagement can be gauged.
The AS Tronic also has provision for two PTOs that can be used, for example, to drive hydraulic pumps to level the crane, or for an emergency steering pump. These PTOs are clutch dependent and available torque is 1,000Nm.
In addition to transmissions other ZF products have applications in cranes and much development work is going on in these areas. Liebherr’s LTM 1100/2, among others, has a ZF steering system, for example. In future an electronically controlled steer by wire system, already in production for rear axles of trucks, could be seen on cranes. Systems that include the front axle such as the SCS (Steering Control System), now under development jointly with Bosch, are currently illegal in Germany and further development work depends on a change in the law. Advantages claimed of the rear axle system include better manouevrability, a smaller turning circle, reduced tyre wear and improved dynamic stability. Additional benefits of a system that includes the front axle are better handling, safety and comfort. Vehicle construction is also simplified.
Advances are also being made in axle systems, and chassis and suspension technology. Independent air suspension and light weight axles with disc brakes are all becoming more widespread.
